1. Field of the Invention
The invention relates to a method of manufacturing a motor vehicle optical module lens, notably intended to generate a cut-off line in the optical beam of satisfactory sharpness.
2. Description of the Related Art
It is known to provide the lighting modules of a motor vehicle with means for blocking the upper part of an optical beam generated by this module to prevent dazzling the drivers of oncoming vehicles or followed vehicles. Such means are typically masks in the focal plane of the lens of the elliptical module or reflecting surfaces known as beam folders.
Such lighting modules are typically lights such as position lights, headlights, fog lights, adaptive driving beams (ADB), motorway driving lights, and generally any lighting beams that feature a cut-off line.
The brightness of the generated beam then features a cut-off line, and this can prove to be a problem. In fact, the beam forms an area of high contrast between, on either side of the cut-off line, an illuminated part of the road and a part of the road that remains dark.
In this case, there is a risk of this area of contrast causing discomfort for the driver of the vehicle emitting the beam if the cut-off is too sharp. In fact, movements of the vehicle that modify its attitude relative to the ground as it travels sweep this area over the road, which accentuates the discomfort caused by the contrast.
To prevent this discomfort, which is particularly significant with lighting modules (also known as “headlights”) that are elliptical and have smooth lenses, some regulations, such as those that apply in the United States of America, impose the transmission of a minimum optical intensity of the lighting beam above the cut-off line. Thus the discomfort caused by the cut-off line is limited in that this cut-off line is less sharp and more diffuse.
To obtain this reduction of the sharpness of the cut-off line, it is known to situate on the output surface of a lens microstructures forming asperities on this output surface so that rays transmitted by these microstructures are transmitted in directions passing above and below the cut-off line, the sharpness of which is thus reduced.
For example, patent application FR 2 925 656 discloses such a lens in which the microstructures take the form of hollows and bosses disposed on the output surface of the lens either randomly (frosting) or in the form of a relatively regular array.
The document FR 2 931 251 discloses an elliptical motor headlight module lens in which areas with an optical diffusion effect are formed on a surface of the lens and divided into a periodic array of individual cells with respective structural elements, which causes targeted diffusion of the light.
Moreover, it is apparent in other examples that the profile of the microstructures is sinusoidal. Although this profile is simple to manufacture, it nevertheless has the drawback of offsetting the position of the maximum contrast that characterizes the position of the cut-off relative to the rest of the beam, or even of generating a second cut-off line in the beam, which leads to ambiguity when carrying out adjustments that is a serious problem with respect to complying with statutory standards, the double cut-off moreover degrading the range of the beam.
What is needed therefore is an improved method of manufacturing a motor vehicle optical module lens.